1. Field of the Invention
The present invention relates to an electrode plate unit and a battery using the same.
2. Description of the Prior Art
In recent years, secondary batteries are becoming used for various applications. In particular, the application as a driving source of an electric car is to be increased in the future under circumstances in which global environmental protection and effective use of energy resources increasingly have been demanded. With such a variation of applications, the further improvement of the battery property and reliability of a secondary battery have been required.
FIG. 14 shows a conventional secondary battery. In this structure, a battery case 51 housing a group of electrode plates 52 and electrolyte is closed by a lid 57 provided with a safety valve 56. As shown in FIG. 15, the group of electrode plates 52 has a structure in which a plurality of positive electrode plates 61 and a plurality of negative electrode plates 62 are laminated alternately via separators 63. The positive electrode plate 61 and the negative electrode plate 62 are formed by filling a substrate with an active material. As shown in FIG. 14, a lead 53 is led out of the positive electrode plate and connected to the positive electrode terminal 54 provided on the lid 57. Similarly, a lead is led out of the negative electrode plate and connected to the negative electrode terminal 55 provided on the lid 57.
Substrates forming each electrode are produced by cutting out a metal plate. Since a punched metal is used for a substrate for the negative electrode plate, little flashing is formed due to the cutting. On the other hand, when a foam metal is used for a substrate for the positive electrode plate, fibrous flashing is likely to be formed due to the cutting work. Therefore, as shown in FIG. 15, there has been a problem in that a flashing 61a that occurs on the end portion of the positive electrode plate 61 passes through the separator 63 and is brought into contact with the negative electrode 62, thereby causing an internal short circuit between the positive and negative electrodes.
Furthermore, in the above-mentioned conventional secondary battery, there is a problem in that since a side face of the group of electrode plates is exposed, when the group of electrode plates is inserted into the battery case for producing a battery, the electrode plate touches the wall surface of the battery case and may be damaged. One possible example of a structure of the secondary battery proposed in order to avoid such a problem is a structure in which an electrode plate unit in which a positive electrode collector plate is connected to one side of the group of electrode plates and a negative electrode collector plate is connected to another side of the group of electrode plates is housed in a battery case together with electrolyte, and the both electrode collector plates are connected to a positive electrode terminal and a negative electrode terminal, respectively. According to this electrode plate unit, since the side face of the group of electrode plates is covered with the collector plate, it is possible to reduce the damage to the electrode plate when the group of electrode plates is inserted into the battery case. In such an electrode plate unit, the group of electrode plates and the collector plate can be connected by welding. By providing the welding places in several places, it is possible to improve the connection strength and collecting efficiency. However, further improvement of the connecting strength between the group of electrode plates and the collector plate and the collecting efficiency are required.